This project is designed to study human immune response to Neisseria gonorrhoeae infections. The primary goals are to investigate the interactions of antibody and complement in bactericidal activity of serum after uncomplicated genital gonococcal infections or with bacteremic gonococcal infections. Initial observations have indicated that an intact complement system, specifically late acting components, are necessary for protection from bacteremic Neisseria infections. Analysis of such data suggests that bactericidal action of serum is more important that the opsonic action of serum in terms of protective function. Sera from patients with uncomplicated genital N. gonorrhoeae infections often is bactericidal for their infecting organisms, at the time of diagnosis - when positive genital cultures are obtained. Patients can become infected with organisms susceptible to the bactericidal action of their previously obtained serum. Although inoculum effect is not well understood, it is likely that the serum bactericidal activity will not be associated with strong protection from naturally acquired genital N. gonorrhoeae infection. The Neisseria gonorrhoeae bactericidal reaction appears to be dependent upon activation of the classical complement pathway although in some circumstances late killing is associated with activation of the alternative pathway, which may be antibody dependent. Further experiments designed to study the interactions of complement and antibody directed against Neisseria gonorrhoeae are currently underway. BIBLIOGRAPHIC REFERENCES: Petersen BH, Graham JA, Brooks GF: Human deficiency of the eighth component of complement: the requirement of C8 for Neisseria gonorrhoeae bactericidal activity. J Clin Invest 57: 283-290, 1976. Brooks GF, Israel KS, Petersen BH: Bactericidal and opsonic activity against Neisseria gonorrhoeae in sera from patients wih disseminated gonococcal infections. J Infect Dis 134:450-462, 1976.